The JAK -STAT (Janus kinase-signal transducer and activator of transcription) signalling pathway that is stimulated by cytokines has been much investigated in haematopoietic cells, but recent data indicate that this pathway is also present and active during neuronal and glial differentiation. Furthermore, it is now clear that growth factors other than the classical cytokines can act through this pathway and that physiological inhibitors of this signalling cascade exist. Thus, the JAKs, the STATs and their specific inhibitors could be molecules with important roles in the CNS.